Deflection properties of an electrostatic electron lens with a shifted electrode

In this paper, the authors discuss a new electron optical component: an electrostatic lens in which one electrode is intentionally shifted laterally, breaking the rotational symmetry. This lens is called a “shift lens.” Usually, a shifted electrode is undesired, and the resulting aberrations are calculated only for the purpose of setting manufacturing requirements. However, the shift lens can be applied as a deflector. Thus, in multibeam systems with an individual microlens for each beam, all beams can be deflected with a single voltage. By giving a different shift to each lens, the deflection can be different for each beam. This allows the creation of a multibeam rotation error corrector. The optical properties of an electrostatic five-electrode lens with a shifted middle electrode are analyzed in this paper. For describing the optical properties of the shift lens, a simple mirror symmetric model in combination with Taylor polynomials is used. This model is then verified with a newly developed ray-tracing program, and the obtained aberrations are discussed. The middle electrode is shifted over a range of 1%–20% of the diameter of the lens. The authors have found dependences of deflection, defocus, astigmatism, and second order on shift distance and excitation. The authors expect the shift lens to be a useful new optical component, especially in multibeam systems.